1. Field of the Invention
The present invention relates to a new thermoplastic resin composition which can be made into molded articles by injection molding, extrusion molding, or the like.
2. Related Art
Polyphenylene ether resin is generally superior in heat resistance, hot water resistance, dimensional stability, and mechanical and electrical properties. Unfortunately, these advantages are offset by its poor moldability (due to high melt viscosity), poor chemical resistance, and low impact resistance.
One well-known way of improving the molding properties of polyphenylene ether resin by lowering its melt viscosity, while retaining its outstanding properties, is to blend it with polystyrene resin. However, the resulting blend is not improved in chemical resistance.
By contrast, propylene polymer is superior in moldability, toughness, water resistance, and chemical resistance. Moreover, it has a low density and is low in price. Therefore, it has found general use as a variety of molded articles and film and sheet.
Despite these advantages, propylene polymer still has room for improvement in heat resistance, stiffness, impact resistance, coatability, and adhesion properties. These drawbacks hinder the development of its new applications. Improvement in heat resistance and impact resistance is urgently required.
It is expected from the foregoing that polyphenylene ether and propylene polymer will be blended with each other to give a resin composition which has the features of both and improved moldability and impact resistance. Such a resin composition, if feasible, would find use in a variety of new applications.
In practice, however, they are poor in miscibility and their blend merely gives injection molded articles which suffer from phase separation and are too poor in appearance and mechanical properties to be of practical use. Therefore, there is a strong demand in the market for a resin composition which exhibits high impact resistance and outstanding weathering performance while retaining the good heat resistance characteristic of polyphenylene ether.
To meet this demand, the present inventors proposed a thermoplastic resin composition having outstanding heat resistance and mechanical properties which is composed of a polyphenylene ether, a modified propylene polymer which is obtained by grafting a styrene-based monomer alone or in combination with a monomer copolymerizable with a styrene-based monomer, and a rubbery substance. (See Japanese Patent Application No. 287129/1988 and Japanese Patent Laid-open No. 207349/1989.)
This thermoplastic resin composition provides molded articles which exhibit high heat resistance and good mechanical properties but lack sufficient stiffness and dimensional stability. Thus it still has room for improvement in this respect.
With the foregoing in mind, the present inventors carried out a series of researches to develop an effective technology. As the result, they found a new resin compound which is superior in processability and provides molded articles having improved impact resistance, heat resistance, stiffness, dimensional stability, paintability, appearance, and smoothness. This led to the present invention.